Incontinence detection devices are used in health care facilities to detect if an occupant of a bed, i.e. a patient, has suffered an incontinence event (accidental discharge of urine and/or liquid fecal matter). Detection of incontinence is important for at least the following reasons. First, a caregiver who knows that a patient is subject to incontinence may be obligated to periodically wake the patient to determine if he has suffered an incontinence event. If an incontinence event has not occurred, the caregiver's intervention has needlessly interrupted the patient's sleep and occupied the caregiver's time. Second, the presence of fecal matter and urine on the bed is unsanitary and should be cleaned up as soon as possible. Third, prolonged exposure of the patient's skin to the moisture arising from the incontinence event increases the risk that the patient will develop a pressure ulcer. Early detection improves the likelihood that a caregiver will take corrective action (drying the patient and replacing soiled sheets and blankets) before the presence of the moisture can compromise the integrity of the patient's skin. Conversely, a detection system that issues numerous false alarms can discourage caregivers from responding as quickly as is desirable, and may even discourage caregivers from using the pad.
One type of incontinence detection system includes a pad that a caregiver places on the mattress of the bed, underneath the patient. The pad has a Radio Frequency Identification (RFID) circuit comprised of a passive RFID tag connected to electrical conductors that branch out from the tag. The system also includes an RFID reader which interrogates the tag.
The tag responds to interrogations from the reader by generating a return signal whose information content includes a moisture status indicator. When the pad is dry the RFID circuit is open, and the moisture status indicator in the return signal indicates the dry status of the pad. When an incontinence event occurs, the liquid moisture closes the circuit so that the moisture status indicator indicates the wet status of the pad.
The reader is adapted to communicate with a destination other than the tag. Upon receiving the return signal, the reader can make a report to the destination of the wet/dry status of the pad. In one example the destination is a light switch and the report is a signal that operates the switch so that the light indicates the status of the pad. In another example the destination is a nurse call system and the report is a message displayed at a nurse station.
One difficulty with such a system is that patient movement can shift the position of the pad on the bed, and/or the patient may move relative to the pad and the reader. Consequently the spatial relationship among the patient, the reader, and the tag may change, or the patient's position may interfere with clear communication between the reader and the tag. This can result in the interrogation signal from the reader being too weak to be useful when it arrives at the tag or the return signal from the tag being too weak to be useable by the reader.
In principle, difficulties arising from weak signals can be addressed by generating a more powerful signal at the reader and producing a correspondingly more powerful return signal from the tag. However in practice, the use of a more powerful signal can cause the RFID circuit to indicate a false wet condition. Moreover, a more powerful signal may expose the patient to more radio frequency (RF) energy than is prudent or more than is permitted by safety regulations.
Therefore, it is desirable to provide an incontinence detection device that reliably detects actual incontinence events, is not likely to produce false alarms (erroneous indications that the pad is wet) and that operates at modest levels of RF energy.